1. Field of the Invention
This invention relates to refrigeration systems and in particular to means for controlling the delivery of refrigerant fluid from the compressor thereof.
2. Background Art
In conventional refrigeration systems, a compressor is utilized to compress the refrigerant which has vaporized in the evaporator, and the compressed refrigerant is passed through a condenser so as to be returned to the evaporator in liquid form. The operation of the compressor is controlled by a thermostat which senses the temperature of the space being refrigerated so as to cycle the refrigeration system as needed to maintain a desired temperature range. When the compressor is de-energized by the thermostat as a result of the sensed temperature dropping to the desired preselected temperature, some refrigerant may flow from the condenser to the evaporator. This flow is undesirable as it tends to warm the evaporator. It also permits the liquid refrigerant in the capillary leading to the evaporator to gasify, thereby requiring a period of liquid delivery to the capillary upon subsequent restarting of the compressor before normal operation of the refrigeration system is again obtained.
In one conventional form of refrigeration system, the compressor comprises a rotary compressor which is capable of starting under relatively high discharge pressures. However, where such discharge pressures are caused to be extremeley high, such as under high ambient temperature conditions, it is desirable to provide some means for reducing the excessive pressure.
A number of different approaches have been taken in the background art relative to controlling the flow of refrigerant in refrigeration systems. Illustratively, as shown in U.S. Pat. No. 1,836,072 of Harry B. Hull, a refrigerating apparatus includes a control which senses the temperature of the condenser for modulating the refrigerant flow from the condenser to the evaporator. The functioning of the valve is to maintain a constant evaporator pressure.
In U.S. Pat. No. 2,245,454, Marshall W. Baker shows a refrigerating apparatus utilizing a valve between the capillary and evaporator for sensing the pressure of the evaporator and utilizing this pressure in controlling the refrigerant flow.
Lloyd A. Staebler et al, in U.S. Pat. No. 2,687,020, shows a refrigeration apparatus having valve means for switching refrigerant flow between two different capillary tube-evaporator systems. This system maintains a refrigerant flow circuit open at all times either to the freezer evaporator or the refrigerator evaporator.
In U.S. Pat. No. 3,199,306 of Bruce M. Paul, a refrigeration apparatus control circuit is shown having a valve upstream of an expansion device. The valve is controlled by the suction line temperature and is opened whenever a switch responsive to the suction line temperature calls for cooling. The circuit is arranged to concurrently start the compressor and open the control valve.
Glendon A. Raymond, in U.S. Pat. No. 3,677,028 shows a refrigeration system having a solenoid-operated valve upstream of the capillary, which is caused to open and close as a function of the compressor energization.
In U.S. Pat. No. 3,722,228, Russell T. Smith shows a refrigeration system wherein a capillary is connected between the condenser and evaporator, permitting flow therebetween at all times. Smith shows a flow control valve for controlling both the inlet and outlet of the compressor so as to prevent refrigerant migration during the shutdown interval.
Ettore Funaro, in U.S. Pat. No. 3,884,663 shows a refrigeration system having a normally closed solenoid valve connected between the condenser and a plurality of parallel connected capillary tubes. The valve is cycled with the compressor.
In U.S. Pat. No. 4,067,203, Joseph L. Behr shows a refrigeration system having an electronically controlled expansion valve maintaining the evaporator thereof in flooded condition. In one form, the control includes means for sensing the temperature of the compressor sump, the ambient air, etc., for opening the expansion valve. In another form, the control senses the temperature of two points of the evaporating coil. The control effectively functions to permit the system to operate with the evaporator in a flooded stage without damage to the compressor.